Dynamic aspects of the surface of a palladium on alumina catalyst used in combustion of methane
(2005)
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- Abstract
- Dynamic phenomena occurring on the surface of Pd-supported catalysts during the catalytic combustion of methane (CCM) were investigated. Several key-parameters involved in such surface dynamic phenomena were identified, such as (i) the nature of the support, (ii) the role of CO2, (iii) the oxidation state of the active phase, (iv) the surface state of the catalyst, (v) the reaction mechanism, (vi) the influence of H2 in the CCM feed, and (vii) the structure sensitivity of the active phase. The influence of CO2 upon the CCM process depends on the nature of the support: inhibition is observed on Pd/ã-Al2O3, whereas activation is observed for ceria-zirconia supported catalysts. The inhibition of the alumina-supported catalyst is not due to formation of carbonates species, while on Ce-Zr-O based catalysts, dissociation of CO2 on the support would be responsible for the activation process. The Pd/ã-alumina catalyst progressively activates during the CCM reaction. This activation phenomenon is related to some sintering of the palladium phase on the alumina surface, which would induce structural changes in the palladium particles. Such restructuring may be responsible for the activation process by facilitating the formation of an active oxygen layer on the PdO surface. Indeed, under reaction conditions, the surface of palladium is always in an oxidized form and would be covered with a layer of highly reactive oxygen species. CH4 can react with these surface O species, producing CO and creating surface O vacancies on the external layer of the palladium particle surface. These O vacancies in the external layer can be reoxidized either by gaseous O2 or by oxygen coming from the bulk of the PdO particles, if there is a lack in gaseous O2. The CO intermediate species can (i) adsorb on the surface of reduced palladium, (ii) react with the alumina support or (iii) be oxidized into CO2, depending on the temperature and on the oxygen partial pressure. Experiments adding H2 in the CCM feed were in good agreement with this hypothesis.
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Demoulin, O. (2005). Dynamic aspects of the surface of a palladium on alumina catalyst used in combustion of methane. https://hdl.handle.net/2078.5/98467